Many types of centrifuge units in the prior art are designed for separating substances of varying density by centrifugal force. These centrifuges, for the most part, comprise an outer housing with an inner rotating rotor which is spun by a motor driven spindle. Carriers containing the samples are located on the circumference of the rotor. The centrifuge units are generally provided with a latchable lid that remains latched during an operation cycle of the unit in which the substances are separated and until the rotor stops rotating.
The prior art centrifuge units and the procedures used in washing contaminants from such units are generally deficient in the manner in which biological hazardous substances are handled. More specifically, it has long been known that in handling blood containing hepatitis that some safety precautions are needed. Such precautions in the past have involved the use of masks, gowns, and gloves by human operators to prevent physical exposure to such biological hazardous substances. No successful schemes have been provided by the prior art to completely remove the operator from close proximity with these contaminants. More specifically, with the prior art units the operator is normally placed in relatively close contact with contaminants during the washing, flushing and draining of the unit. The cleaning and sterilizing procedures for the prior art units invariably involve the operator opening the lid of the unit and subsequently scrubbing the interior of the unit and/or sterilizing the same with a sterilizing agent. Even with the use of protective coverings, the operator assumes definite risk during the cleaning process. These risks and others like them have led the government and the industry to be increasingly concerned with biological hazard containment and have recently been responsible for the introduction of new regulations and guidelines. Generally, the prior art centrifuges do not possess sufficient biological containment features to meet these new regulations and guidelines. Such deficiencies in biological hazard containment will be discussed hereinafter.
Generally, the prior art centrifuge units may be divided into sealed refrigerated units and non-refrigerated units. Some of the non-refrigerated units have at least one aperture formed in the lid which allows for the suction of air into the unit. This negative pressure is produced by the spinning rotor and is used to produce an air flow to cool the motor portion of the system. Also, the aperture defines an open system which allows the system to be drained at the end of a run. With the prior art refrigerated units, there are generally no apertures formed in the lids in that a closed system having a cooled, controlled environment must be maintained. Consequently, the refrigerated units of the prior art define an atmospherically closed system in which no outside ambient air is introduced during the operation cycle of the unit. On the other hand, the non-refrigerated units of the prior art normally define an atmospherically open system in which a continuous flow of ambient air is maintained into the unit during the operation cycle of the unit.
Normally, cleaning and/or sterilizing procedures for refrigerated and non-refrigerated units of the prior art include opening the lid and introducing water and/or a cleaning agent or sterilizing agent into the interior. After manually scrubbing the unit to clean the same, the remaining cleaning liquid collects in a guard bowl positioned under the rotor. This liquid can be removed by flushing the same through a gravity drain formed in the guard bowl. In some prior units, an additional step is introduced into the cleaning process after manual cleaning, such step including operating the rotor so as to stir the cleaning liquid in the guard bowl while draining such liquid. In the prior art refrigerated units, the flushing through a drain normally requires that the lid be kept open. In summary, the prior art cleaning and/or sterilizing procedures call for the opening of the lid for the introduction of the cleaning liquid and/or sterilizing agent and for manual cleaning, thereby exposing the operator in some cases to biological hazards.
Another inherent problem in the prior art centrifuge units is that the non-refrigerated units may release contaminants through the previously described aperture in the lid after the unit has shut off. More specifically, while operating, the inflowing ambient air into the unit caused by the negative pressure therein prevents contaminants from escaping. However, upon intentionally or unintentionally stopping the unit, negative pressure ceases and contaminants may escape.
Federal government regulations require some form of calibration, which is not interior of the units, be used for providing a dynamic indication of actual rotor speed (RPM). Hence, speed measuring devices must be independent of the centrifuge unit, or to put it another way, not built into the unit.
The centrifuge units of the prior art normally have as input data the following: (1) speed in rotations per minute (RPM) and (2) time for the operation cycle. The following mathematical relationship is well known in the art:
RCF=1.119 (10.sup.-5) R(N).sup.2, where PA1 RCF=Relative centrifugal force in kilograms, PA1 N=RPM, and PA1 R=Sample tip radius in centimeters.
The relative centrifugal force (RCF), if excessive, can impair proper sample separation and can cause damage to the sample, sample carrier rotor to spindle. Sample tip radius (R) can vary substantially depending upon the rotor and carrier being used. Hence RCF better correlates than RPM as a measurement for avoiding the above described undersirable effects. As a result, the diagnostic companies have initiated the practice of specifying maximum tolerances on tubes and samples in terms of RCF. Moreover, centrifuge procedures are beginning to refer to an applied constant RCF level as one of the parameters rather than, or at least in addition to RPM. An operator of a state of the art centrifuge unit must use the above equation or a chart to come up with the RCF in determining a proper RPM input. Since this necessary step frequently is not understood or simply ignored, machine and sample damage and improper sample separation are common.
It is scientifically known that, in addition to RCF, accumulative RCF (G-time) correlates closely to degree and quality of separation of a specimen. Referring to FIG. 5 of the drawings, a typical graph of RCF (G's) versus time is shown for an illustrative centrifuge unit. The area of the graph represents accumulative RCF. As already explained, the standard machine inputs for prior art units is time (T) for the operation cycle and a constant RPM. Through the previously stated equation, the constant RPM for a given sample tip radius can be used to calculate a constant RCF. The constant RCF is illustrated by the horizontal portion of the graph of FIG. 5 between t.sub.A and t.sub.B. In practice, the time T input will correspond to T=t.sub.B in FIG. 5. After T=t.sub.B, it is normal to allow the centrifuge rotor to coast to a stop or, alternatively, apply a braking action to expedite stoppage of the rotor. The inputted values of time T and constant RPM are based on diagnostic procedures which presuppose that the accumulative RCF will be equal to the heretofore mentioned constant RCF.times.t.sub.B. However, due to the acceleration ramp (before t.sub.A) and deceleration ramp (after t.sub.B) of the graph of FIG. 5, the area of the graph (actual accumulative RCF) rarely is equal to the prescribed (constant RCF.times.t.sub.B) upon which the input values are based. Therefore, even though the centrifuge unit can be operating at a proper level of RCF, the total accumulative RCF may deviate sufficiently from the desired value so as to give poor separation results.
It is of further interest to note that it is a common practice in the art to vary the length of time for deceleration of the rotor by applying a braking force instead of just allowing the unit to coast to a stop. Any estimate of the accumulative RCF must take this into account.
In summary, a given quantity of accumulative RCF at a known, controlled RCF is more effective in separating a sample than the same accumulative RCF at an arbitrary unknown RCF. The total accumulative RCF relates to the effectiveness of separating a sample. Consequently, a proper level of RCF and a proper amount of accumulative RCF must be applied to a sample in order to achieve a desired separation.